Control channel detection scheme

ABSTRACT

A method for detection of a control channel includes receiving data transmitted via the control channel. A control channel receive quality is estimated based on a metric difference between a metric of a known final trellis state and a minimum metric amongst the metrics of the trellis states based on the received data. It is decided whether or not to detect the control channel depending on the estimated control channel receive quality.

FIELD OF THE INVENTION

The invention relates generally to the technique of control channeldetection in communications systems.

BACKGROUND OF THE INVENTION

In many communications systems, in particular wireless mobilecommunications systems, one or more control channels are transmitted inaddition to data channels. Such a control channel may containinformation which must be known at the receiver before starting thedetection of the data channel. Therefore, a fast detection of thecontrol channel at a receiver is important for obtaining a high overallsystem performance.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention are made more evident by way of example in thefollowing detailed description of embodiments when read in conjunctionwith the attached drawing figures, wherein

FIG. 1 is a schematic block diagram of a decoding and detection unit ofa receiver according to a first embodiment;

FIG. 2 is a schematic timing diagram of shared control channels and datachannels;

FIG. 3 is a schematic illustration of a shared control channel encodingprocess;

FIG. 4 is a schematic block diagram of a decoding and detection unit ofa receiver according to a second embodiment;

FIG. 5 is a graph illustrating an average bit error rate afterre-encoding and an average control channel quality for a control channelwhich is not intended for a receiver; and

FIG. 6 is a graph illustrating an average bit error rate afterre-encoding and an average control channel quality for a control channelwhich is intended for a receiver.

DETAILED DESCRIPTION OF THE INVENTION

In the following, embodiments of the invention are described withreference to the drawings, wherein like reference numerals are generallyutilized to refer to like elements throughout the description. In thefollowing description, for purposes of explanation, numerous specificdetails are set forth in order to provide a thorough understanding ofone or more aspects of embodiments of the invention. It may be evident,however, to one skilled in the art that one or more aspects of theembodiments of the invention may be practiced with a lesser degree ofthese specific details. In other instances, known structures and devicesare shown in a simplified representation in order to facilitatedescribing one or more aspects of the embodiments of the invention. Thefollowing description is therefore not to be taken in a limiting sense,and the scope of the invention is defined by the appended claims.

In mobile communications systems, a transmitter transmits user data viauser data channels and control data via one or more control channels toa receiver. The transmitter may be a base station of the wirelesscommunications system and the receiver may be a mobile station of thewireless communications system. Such channels from a base station to amobile station are termed downlink channels. However, the followingdescription may also relate to data channels and control channels fortransmission of user data and control information, respectively,transmitted from a mobile station to a base station. Such channels arereferred to as uplink channels. Herein and in the related art, a mobilestation will be referred to as a User Equipment (UE).

Wireless communications systems according to the following descriptionmay be CDMA (Code Division Multiple Access) systems in one embodiment.However, also other types of multiple access techniques could be used inwireless communications systems considered herein, and all suchvariations and alternatives are contemplated as falling within the scopeof the invention.

A control channel intended for a receiver may contain an Identity (ID)bit sequence of the scheduled receiver. Usually, the ID bit sequence iscontained in a leading part of the control channel transmitted by thetransmitter. For instance, in this leading part of the control channel,the ID bit sequence may be used to mask additional control informationsuch as e.g. information relating to the channelization code and/or themodulation scheme used at the transmitter to generate the user datasignal to be transmitted. Therefore, the detection of the controlchannel may be based on an estimation of the decoding quality of thecontrol channel at the receiver. If the control channel can be decodedwith high (or better to say sufficient) quality, it may be assumed thatthe leading part of the control channel had been masked by the ID bitsequence of the scheduled receiver.

The detection performance of a receiver may be defined in terms of the“probability of missed detection” (P_(md)), i.e. the probability thatthe receiver misses the detection of the part of the control channelcarrying its ID bit sequence, and the “probability of false alarm”(P_(fa)), i.e. the probability that the receiver falsely detects a partof the control channel carrying a different receiver's ID bit sequenceor any other bit, sequence.

Typically, the detection of a control channel is a crucial algorithm forcommunications system performance. Missed detections reduce thecommunications system throughput and false detections triggerunnecessary receptions which will be aborted at a later stage of thereception process. However, this causes waste of terminal resources andpower consumption.

FIG. 1 illustrates a first embodiment of a decoding and detection unit100 of a receiver in a wireless communications system, which may be a UEor a base station. In the following embodiment, without limitation ofthe generality, the receiver is assumed to be part of a UE (i.e. amobile station).

The decoding and detection unit 100 of a receiver contains a firstsection 110 and a second section 120. The first section 110 comprises ade-masking unit 111, a decoder 112, a minimum/maximum unit 113, and adifference unit 114. Control data contained in a downlink controlchannel and user data contained in a downlink data channel are input tothe de-masking unit 111 via input 115. The de-masking unit 111 furtherreceives the ID of the UE under consideration. The part of the controlsequence which is masked by the ID of the scheduled UE is de-masked bythe ID of the UE under consideration. De-masking may be performed by theinverse masking process, e.g. by a sign inversion process based on theUE's ID. Control data and user data are supplied by a demodulator (notshown) of the receiver to the input 115 of the first section 110.

The de-masked part of the control sequence is fed via connection 116 tothe decoder 112. In one embodiment the decoder 112 may be a Viterbidecoder performing channel decoding. Further, the decoder 112 mayperform a de-puncturing operation.

The Viterbi decoder 112 decodes the incoming data, here at first thede-masked leading part of the control channel. As known in the art,Viterbi decoders 112 are used to decode bit sequences which weresubjected to channel encoding at the transmitter.

Viterbi decoding is based on finding the shortest path through a statediagram of an encoder register which is used for channel encoding at thetransmitter. This diagram is known as a trellis diagram. In the trellisdiagram, the states of the encoder register are plotted versus thediscrete time k. According to the Viterbi algorithm, a branch metricwhich represents a measure of the probability of the branch iscalculated for each possible branch between two states (previous staterelating to the time stamp k→destination state relating to the timestamp k+1). The branch metrics are then added to the respective statemetrics (which are frequently also referred to as path metrics in theliterature) of the previous states (ADD). For branches leading to thesame destination state, the sums which are obtained in this way arecompared (COMPARE). That branch to the destination state underconsideration whose sum of the branch metric and state metric of theprevious state is a minimum is selected (SELECT) and forms the extensionof the path leading to this previous state to the destination state.These three basic operations of the Viterbi algorithm are known asACS-(ADD-COMPARE-SELECT) operations.

While from a combinational point of view, the number of paths throughthe trellis diagram increases exponentially as k rises (that is to sayas time progresses), it remains constant for the Viterbi algorithm. Thisis because of the selection step (SELECT). Only one selected path(“survivor”) per destination state is retained and can be continued. Theother possible paths are rejected. Recursive path rejection is theconcept used in the Viterbi algorithm to limit the number of paths whileprogressing through the trellis diagram.

In the following, without limitation of generality, it may be assumedthat the length of the channel encoder register at the transmitter is n.This means that the encoder register has n register cells. In this case,the encoder register may be described by a trellis diagram having 2^(n)states. Thus, the decoder 112 has 2^(n) outputs 117, wherein at eachoutput one state metric (of the 2^(n) state metrics) is output andupdated every time stamp k.

It is now considered a time stamp k_(dec) at which time the part of thecontrol channel containing the de-masked ID of the UE is completelydecoded. This is achieved when the bits of the de-masked ID are alltrellis processed and when the encoder's state is known. The lattercondition (known encoder's state) may be guaranteed by forcing theencoder to a zero state by appending an n bit sequence of zeros to themasked part of the control sequence containing the ID of the scheduledUE. By way of example, if n=8, a tail bit sequence (0,0,0,0,0,0,0,0)forces the channel encoder to its zero state. As a consequence, thestate metric associated with the zero state in the trellis diagram atthe Viterbi decoder 112 should be the minimum state metric amongst allstate metrics at time stamp k_(dec), which is n time stamps later thanthe time stamp corresponding to the last bit of the ID.

In the following, M₀ refers to the state metric at the known finaltrellis state (e.g. at the zero trellis state if a zero tail sequence isused), M_(min) refers to the minimum state metric amongst the statemetrics of the trellis states and M_(max) refers to the maximum statemetric amongst the state metrics of the trellis states at the 2^(n)state metric outputs of the decoder 112 at time stamp k_(dec). M_(min)and M_(max) are determined by the minimum/maximum unit 113 in oneembodiment.

The difference unit 114 calculates the metric differences M₀−M_(min)and, optionally, M_(max)−M_(min). These differences are passed viaconnections 118, 119 to a computing unit 121 located in the secondsection 120 of the receiver 100. In one embodiment the computing unit121 may compute the following ratio of metric differences

$R = {\frac{M_{0} - M_{\min}}{M_{\max} - M_{\min}}.}$

R provides a fair indication of the detection quality of the controlchannel at the UE (or, more generally, at the receiver). R may assumevalues in the range between 0 and 1, and the decoding quality improvesas R gets close to 0. More specifically, as the minimum metric stateshould be the forced zero state, an error-free Viterbi decoding shouldresult in R=0. Due to noise, it may be the case that the forced zerostate is not the state having minimum state metric, i.e. M_(min)<M₀.However, also in this case, the zero state metric MO should at least beclose to the minimum one M_(min). Therefore, R stays small. On the otherhand, when the Viterbi decoding has a substantial number of errors (forinstance for a control channel which is not masked with the ID of the UEunder consideration), the zero state metric M₀ can even be closer to themaximum state metric M_(max). In this case, the ratio R increasesindicating that the control channel is detected with low quality. Thus,the control channel receive quality is related to R and may thus beevaluated on the basis of R.

It is to be noted that the metric difference M_(max)−M_(min) is used forscaling the metric difference M₀−M_(min). The scaling is beneficialbecause Viterbi state metrics increase with the amplitude of thereceived signal, i.e. the SNR (Signal-to-Noise Ratio). Scaling byM_(max)−M_(min) eliminates this influence of signal amplitude to theeffect that R is virtually independent of the amplitude of the receivedsignal. Further, it is known that Viterbi decoders such as e.g. realfixed-point Viterbi decoders scale the accumulated state metrics duringthe forward recursion, for instance by subtracting a constant from allthe state metrics almost every time stamp in order to avoid overflow.Also such internal re-scaling operation of the Viterbi decoder 112 iscanceled out by considering a ratio of metric differences.

It is to be noted that in alternative embodiments the denominator of theratio R may be of a different type, i.e. need not necessarily be adifference M_(max)−M_(min). For instance, also an average metric couldbe used. In this case, however, R would not be limited by 1.

R is passed via connection 122 to a quality comparator 123. The qualitycomparator 123 compares R with a threshold value T. T may e.g. be afixed threshold value in one embodiment. If R is below or equal to thethreshold value T, the control channel is decided to be a controlchannel of sufficient detection quality. Then, the detected controlinformation (e.g. the modulation scheme and/or the channelization code)is output from the second section 120 of the receiver at controlinformation output 124 and the reception of the user data channel istriggered at a first control output 125 enabling user data detection.Otherwise, if R is above the threshold value T, the detected controlinformation is discarded (in FIG. 1, this is illustrated by an openswitch 126 between the Viterbi decoder 112 and the control informationoutput 124) and the detection of the user data channel is inhibited byactivating a control output 127 which disables the detection of the userdata. Thus, it is deciding to detect the control channel (i.e. to useits control information) whenever the detection quality (which may beexpressed e.g. by R⁻¹) is higher than a threshold (in this case T⁻¹).

According to one embodiment the first section 110 of the receiver may beimplemented in dedicated hardware whereas the second section 120 of thereceiver may be implemented in software, e.g. as a General PurposeProcessor (GPP). This solution provides for competitional efficiencybecause in such alternative embodiments all subtractions are performedin hardware, and for high flexibility because the threshold T andprobably further algorithms for deciding about the detection of acontrol channel may be programmable by software.

In FIGS. 2 to 6 a specific embodiment relating to High Speed DownlinkPacket Access (HSDPA) is shown. HSDPA has been introduced in the thirdGeneration Partnership Project (3GPP) Release 5 to provide enhancedsupport for packet data services with improved system throughput andreduced system latency for peak data rates up to 14.4 Mb/s in thedownlink direction from the base station to the UE. Most of thedescription of the embodiment illustrated in FIG. 1 may equally beapplied to the second embodiment and is therefore partly omitted inorder to avoid reiteration. On the other hand, details of the morespecific second embodiment may equally apply to related aspects of thefirst embodiment.

HSDPA supports enhanced features such as shared channel transmission,adaptive modulation and coding (AMC), fast Hybride Automatic RepeatreQuest (HARQ), fair and fast scheduling at the NodeB (i.e. basestation) rather than at the radio network controller (RNC) and Fast CellSide Selection (FCSS). Further, HSDPA introduces a shorter TransmissionTime Interval (TTI) of 2 ms (corresponding to 3 time slots) than in theprevious releases in order to decrease Round Trip Time (RTT) delay.Amongst others, HSDPA introduces new shared and fast-scheduled physicalchannels:

-   -   HS-PDSCH (High Speed Physical Downlink Shared Channel) carries        user data in the downlink direction. It is time shared between        the UEs (i.e. mobile stations). To achieve a peak transfer rate        of 14.4 Mb/s the NodeB can allocate up to 15 HS-PDSCHs to the        same UE.    -   HS-SCCH (High Speed Shared Control Channel) is used by the NodeB        to signal to the scheduled UE to receive HS-PDSCH(s) in the next        TTI. In the meantime, it carries the HS-PDSCH(s) control        information such as channelization codes, modulation schemes        (e.g. QPSK (Quadrature Phase Shift Keying) or 16 QAM (Quadrature        Amplitude Modulation)), transport block size, HARQ process        number, redundancy and constellation version and a new data        indicator. Further, the HS-PDSCH(s) control information contains        an identity (ID) of the UE to which the message is addressed. In        order to schedule several UEs, the NodeB can transmit up to 4        HS-SCCHs simultaneously.

FIG. 2 illustrates the timing of control channels HS-SCCHs and user datachannels HS-PDSCHs. HS-SCCH(s) are sent two time slots in advance thecorresponding HS-PDSCH(s) to allow enough time to the UE to configureitself for receiving the data channels. A first HS-SCCH 201 is addressedto a first UE denoted as UE1 and a second HS-SCCH 202 is addressed to asecond UE denoted as UE2. Each HS-SCCH 201, 202 is divided into twofunctional parts: in Part 1, which spans over one time slot, the NodeBtransmits urgent information such as the channelization codes and themodulation schemes while in Part 2, which spans over two time slots, theremaining (less time critical) information is transmitted. In theexample illustrated in FIG. 2, two HS-SCCHs 201, 202 are transmittedsimultaneously to UE1 and UE2. Two time slots later, i.e. at a timeinstance in the center of Part 2, UE1 and UE2 simultaneously start todetect user data channels HS-PDSCHs. More specifically, UE1 detectsthree HS-PDSCHs and UE2 detects four HS-PDSCHs during a first TTI of 2ms (3 slots) referred to as TTI1. For the next transmission timeinterval TTI2, only control information in form of a HS-SCCH 203 for UE2is provided. Thus, during TTI2, only UE2 is active and detects 7HS-PDSCHs. For TTI3, the NodeB only supplies control information in formof a HS-SCCH 204 for UE1. Therefore, during TTI3, only UE1 is active anduses 5 HS-PDSCHs. This process of providing demodulation information byHS-SCCHs dedicated to a specific UE and demodulating the correspondingHS-PDSCHs in UE1 and/or UE2 continues during subsequent transmissiontime intervals TTI4, TTI5.

FIG. 3 illustrates one embodiment of HS-SCCH encoding. The abbreviationsused in FIG. 3 are:

-   -   CCS: Channelization Code Set (7 bits)    -   MS: Modulation Scheme (1 bit)    -   TBS: Transport Block Size (6 bits)    -   HAP: Hybrid-ARQ Process (3 bits)    -   RV: Redundancy and constellation version (3 bits)    -   ND: New date indicator (1 bit)    -   CRC: Cyclic Redundancy Check (16 bits)    -   UE ID: User Equipment Identity (16 bits)        A HS-SCCH comprising Part 1 having 40 bits and Part 2 having 80        bits is denoted by reference number 301. As already mentioned        HS-SCCH 301 spans over three times slots. In Part 1, CCS and MS        information 302 are convolutionally encoded and masked (by an        XOR operation) with the encoded 16-bits ID 303 of the scheduled        UE (referred to as UE ID). In Part 2, TBS, HAP, RV and ND        information 304 are convolutionally encoded together with a        Cyclic Redundancy Check (CRC) masked with the UE ID. The same        ⅓-rate convolutional code with 256 states is used in Part 1 and        Part 2 encoding. Puncturing is used to reduce the number of bits        of the convolutionally encoded UE ID information 303,        convolutionally encoded CSS and MS information 302 and        convolutionally encoded TBS, HAP, RV, ND, CRC and UE ID        information 304, 305 to reduce the number of bits. Up to 4        HS-SCCHs addressing different UEs can be simultaneously        transmitted from the serving HS-DSCH NodeB. Thus, each UE has to        monitor all 4 HS-SCCHs in order to allow for a fast detection of        the use of its UE ID in Part 1 in each HS-SCCH 301. Further, in        connection with the embodiments described herein, the content of        3GPP TS 34.121 Release 5 is incorporated by reference into this        document.

Thus, referring also to FIG. 2, after receiving Part 1 of all theHS-SSCH(s), the UE has only one time slot to make the decision: if oneof the HS-SSCH(s) employing its UE ID is detected, the UE shouldconfigure the reception of the HS-PDSCH(s) with the decoded CCS and MSof the detected HS-SCCH.

FIG. 4 illustrates a decoding and detection unit 400 of a receiveraccording to a second embodiment. This receiver is adapted to providefor a fast detection of HS-SCCH(s) in HSDPA or, more generally, in amobile communications system providing a plurality of shared controlchannels. The decoding and detection unit 400 comprises first sections410.1, 410.2, . . . , 410.4 which may be implemented in dedicatedhardware and a second section 420 which may be implemented in softwaree.g. as a GPP. The first sections 410.1-410.4 are configured to detectthe four shared control channels HS-SCCH#1-HS-SCCH#4. The sections410.1-410.4 may be implemented in one hardware instance which can bemultiplexed in time according to the number of monitored controlchannels according to one embodiment. Instead, the plurality of firstsections 410.1-410.4 may be also implemented in parallel hardware. Thesecond section 420 is typically implemented in one GPP which is fed bythe e.g. time multiplexed outputs of the four first sections410.1-410.4.

The implementation and operation of each first section 410.1-410.4 aresimilar to the implementation and operation of the first section 110illustrated in FIG. 1, and the description thereof is analogouslyapplicable to first sections 410.1-410.4. Each first section 410.1-410.4comprises a de-masking unit 411, a decoding unit 412, a minimum/maximumunit 413 and a difference unit 414 which correspond to units 111, 112,113 and 114 of FIG. 1, respectively. Here the 16-bit UE ID isconvolutionally encoded and punctured in UE processing unit 431according to the Part 1 generation scheme of a HS-SCCH shown in FIG. 3.A bit sequence which is coming from a demodulator arranged in the signalpath upstream of the first sections 410.1-410.4 is input via inputconnection 415.1 to the de-masking unit 411. There, it is de-masked bysign inversion dependent from the output of the UE processing unit 431.

Similar to the first embodiment, the example viterbi decoder 412provides a final accumulated metric for each trellis state at the end ofthe forward recursion performed for decoding Part 1 of the HS-SCCH 301.Referring to FIG. 3, both the UE ID information 303 and the CCS and MSinformation 302 are terminated by a 8-bit tail sequence 303 t. This8-bit tail sequence may be (0,0,0,0,0,0,0,0), thus forcing the 8-bitregister of the channel encoder to the zero state at the end of encodingthe Part 1 of HS-SCCH 301. Of course, any other state known to thereceiver could be chosen, and such alternatives are contemplated by theinvention. As state metrics computed by a Viterbi decoder 112, 412 mayreflect the Euclidian distance between the received bit sequence and thebit sequence corresponding to the most likely path through the trellisdiagram, the metric of the zero state should be the minimum metricamongst all metrics computed by the Viterbi decoder 412 at the end ofthe Part 1 decoding forward recursion. Therefore, as already explainedfurther above, the metric difference M₀−M_(min) is a measure of thequality of detection of the HS-SCCH under consideration. In order toavoid fixed-point problems (e.g. an overflow) during Viterbi decoding,the state metrics are typically scaled during the forward recursion bysubtracting a constant to all state metrics every or almost every timestamp. For example, the minimum branch metric computed at each timestamp may be subtracted from all state metrics. It is to be noted thatsuch scaling is typically different for decoding different HS-SCCHs,i.e. among decoder units 412 which decode different control channels.

The difference units 414 output metric differences M₀−M_(min) andM_(max)−M_(min) for each HS-SCCHs. These metric differences are fed intocomputing units 421.1-421.4, which are implemented in software in oneembodiment. In other words, the second section 420 (e.g. a GPP) computesin a time multiplexed fashion ratios R for all HS-SCCHs which arepresently detected.

The ratios R associated with the qualities of the detected HS-SCCHs areinput to a control channel selection unit 428. The control channelselection unit 428 may be implemented by a minimum algorithm selectingthe ratio R which is smaller than all other ratios R delivered to thecontrol channel selection unit 428. This ratio R_(min) is passed to aquality comparator 423 having the same functionality as qualitycomparator 123 of the first embodiment. Further, a HS-SCCH indexdenoting the HS-SSCH having the minimum R (i.e. R_(min)) is output fromthe control channel selection unit 428 and passed to a selector 426.

The operation of the second section 420 is similar to the operation ofthe second section 120 illustrated in FIG. 1, and the descriptionthereof is analogously applicable to second section 420. Briefly, ifR_(min) is greater than the (e.g. fixed) threshold T, the detectionquality of all HS-SCCHs is too poor and no detection of a HS-PDSCH isinitiated. In this case, a control output 427 is activated. Otherwise,if R_(min) is below or equal to the threshold T, a control output 425(corresponding to control output 125 of the first embodiment) is enabledand reception of the corresponding HS-PDSCH is initiated. In this case,the selector 426 is activated by the quality comparator 423 and the CCSand MS information contained in Part 1 of the selected HS-SCCH indexedby the control channel selection unit 428 is provided at output 424 ofthe second section 420. On the basis of this information, the receiverconfigures itself to start user data reception from the HS-PDSCHassociated with the selected HS-SCCH one time slot later.

It is to be noted that the scaling of the metric difference M₀−M_(min)by the metric difference M_(max)−M_(min) in the denominator of ratio Rin one embodiment allows to compare the ratios R obtained from differentHS-SCCHs in the control channel selection unit 428, because thisdecoder-individual scaling further eliminates the use of differentscaling factors in Viterbi decoding of different HS-SCCHs.

The software-hardware split illustrated in FIGS. 1 and 4 should beunderstood to be exemplary. For instance, another embodiment possibilityis to implement the minimum-maximum operation performed by theminimum/maximum units. 113, 413 and the subtraction operation performedby the difference units 114, 414 in software. In this case, the firstsection 110, 410.1-410.4 may be implemented by standard hardware andsubstantially all computation for control channel quality estimation isdone in software. In another embodiment, the computing units 121,421.1-421.4 and/or others of the units in the second sections 120, 420may be implemented in hardware.

The second embodiment provides for a reliable and fast HS-SCCH detectionwithout adding more complexity, i.e. hardware modules, to the receiver.The proposed HS-SCCH detection algorithm is based on the Viterbidecoders final state metrics which are exploited at the end of the Part1 decoding. This approach provides for a finer tuning of the thresholdand therefore for a better P_(md) and P_(fa) joint optimization comparedto a conventional HS-SCCH detection and selection approach which isbased on a BER (Bit Error Rate) channel quality estimation of HS-SCCHs.Such BER quality estimation involve re-encoding of the decoded datastream and comparing the re-encoded data with the received data prior toViterbi decoding. If re-encoded data is substantially the same as thedata before Viterbi decoding, the corresponding HS-SCCH is rated to havea high detection quality. Otherwise, the detection quality of the.HS-SCCH is rated to be low and the data detection of the correspondinguser data channel HS-PDSCH is inhibited. FIGS. 5 and 6 illustrate graphswhich compare this conventional approach (“average BER afterre-encoding”) with the approach described herein (“average R”). AverageBER after re-encoding and average R are plotted versus Eb/NO (the energyper bit to noise power spectral density ratio) in units of dB. FIG. 5shows the results when a HS-SCCHs not intended for a UE is detected andFIG. 6 shows the results when a HS-SCCH is detected which is intendedfor the UE. The conventional approach suffers from low sensitivity dueto the limited number of bits available before channel decoding. Incontrast thereto, using average R discrimination, a higher sensitivityand thus a considerably better P_(md) and P_(fa) joint optimization ispossible.

It is to be noted that the detection of one or more control channels asdescribed above is applicable to a wide range of receivers, including3GPP-receivers, HSDPA-receivers, LTE-receivers (Long Term Evolution)etc. Further, the concepts described above by way of example in relationto downlink channels are also applicable to uplink control channels anduser data channels, i.e. to a receiver located in a base station. Forinstance, HSUPA-receivers (High Speed Uplink Packet Access) may beimplemented that way for enhanced detection of one or more uplinkcontrol channels transmitted by UEs.

Although the invention has been illustrated and described with respectto one or more implementations, alterations and/or modifications may bemade to the illustrated examples without departing from the spirit andscope of the appended claims. In particular regard to the variousfunctions performed by the above described components or structures(assemblies, devices, circuits, systems, etc.), the terms (including areference to a “means”) used to describe such components are intended tocorrespond, unless otherwise indicated, to any component or structurewhich performs the specified function of the described component (e.g.,that is functionally equivalent), even though not structurallyequivalent to the disclosed structure which performs the function in theherein illustrated exemplary implementations of the invention. Inaddition, while a particular feature of the invention may have beendisclosed with respect to only one of several implementations, suchfeature may be combined with one or more other features of the otherimplementations as may be desired and advantageous for any given orparticular application. Furthermore, to the extent that the terms“including”, “includes”, “having”, “has”, “with”, or variants thereofare used in either the detailed description and the claims, such termsare intended to be inclusive in a manner similar to the term“comprising”.

1. A method for detection of a control channel, comprising: receivingdata transmitted via a control channel; estimating a control channelreceive quality based on a metric difference between a metric of a knownfinal trellis state and a minimum metric amongst the metrics of thetrellis states, the metrics associated with the received control channeldata; and deciding whether or not to detect the control channel based onthe estimated control channel receive quality.
 2. The method of claim 1,wherein the control channel receive quality comprises a ratio of themetric difference and another metric difference, the another metricdifference being associated with the minimum metric and a maximum metricamongst the metrics of the trellis states.
 3. The method of claim 2,wherein the control channel receive quality is related to the expressionR=(M₀−M_(min))/(M_(max)−M_(min)), wherein M₀ is the metric of the knownfinal trellis state, M_(min) is the minimum metric amongst the metricsof the trellis states and M_(max) is the maximum metric amongst themetrics of the trellis states.
 4. The method of claim 1, whereindeciding whether or not to detect the control channel comprises:comparing the control channel receive quality with a threshold value;and deciding to detect the control channel if the control channelreceive quality is higher than the threshold value.
 5. The method ofclaim 4, further comprising: deciding to not detect the control channelif the control channel receive quality is below the threshold value. 6.The method of claim 1, wherein data transmitted via a plurality ofcontrol channels is received, further comprising: estimating the controlchannel receive qualities of the plurality of control channels;comparing the computed control channel receive qualities with each otherto determine the control channel having the maximum control channelreceive quality; and deciding whether or not to detect the controlchannel having the maximum control channel receive quality.
 7. Themethod of claim 6, wherein the control channels of the plurality ofcontrol channels are high speed shared control channels of a wirelesscommunications system.
 8. A receive unit for detecting a controlchannel, comprising: a receiver configured to receive data transmittedvia a control channel; a channel quality estimator configured to computea control channel receive quality based on a metric difference between ametric of a known final trellis state and a minimum metric amongst themetrics of the trellis states, wherein the metrics are associated withthe received control channel data; and a deciding unit configured todecide whether or not to detect the control channel based on theestimated control channel receive quality.
 9. The receive unit of claim8, wherein the channel quality estimator is configured to compute thecontrol channel receive quality as a ratio of the metric difference andanother metric difference, wherein the another metric difference isassociated with the minimum metric and a maximum metric among themetrics of the trellis states.
 10. The receive unit of claim 9, whereinthe channel quality estimator is configured to computeR=(M₀−M_(min))/(M_(max)−M_(min)), wherein R is related to the controlchannel receive quality, and wherein M₀ is the metric of the known finaltrellis state, M_(min) is the minimum metric amongst the metrics of thetrellis states, and M_(max) is the maximum metric among the metrics ofthe trellis states.
 11. The receive unit of claim 8, wherein thedeciding unit comprises: a threshold comparator configured to comparethe computed control channel receive quality with a threshold value,wherein the deciding unit is further configured to decide to detect thecontrol channel if the control channel receive quality is higher thanthe threshold value.
 12. The receive unit of claim 11, wherein thedeciding unit is further configured to decide not to detect the controlchannel if the control channel receive quality is below the thresholdvalue.
 13. The receive unit of claim 8, wherein the receiver isconfigured to receive data transmitted via a plurality of controlchannels and the channel quality estimator is configured to computecontrol channel receive qualities of the plurality of control channels,further comprising: a quality comparator configured to compare thecomputed control channel receive qualities with each other to determinethe control channel having the maximum control channel receive quality,and wherein the deciding unit is configured to decide whether or not todetect this control channel having the maximum control channel receivequality.
 14. The receive unit of claim 8, wherein a first section of thechannel quality estimator which is configured to compute the metricdifference is implemented in hardware.
 15. The receive unit of claim 8,wherein a second section of the channel quality estimator which isconfigured to compute the control channel receive quality based on themetric difference is implemented in software.
 16. The receive unit ofclaim 8, wherein the deciding unit is implemented in software.
 17. Amethod for selection of a control channel from a plurality of controlchannels, comprising: receiving data transmitted via the plurality ofcontrol channels; estimating a control channel receive quality based ona metric difference between a metric of a known final trellis state anda minimum metric amongst the metrics of the trellis states for each ofthe plurality of control channels, wherein the metrics are associatedwith the received data of each respective control channel; and selectingone of the plurality of control channels based on an evaluation of thecontrol channel receive qualities.
 18. The method of claim 17, whereinthe control channel receive quality comprises a ratio of the metricdifference and another metric difference, the another metric differencebeing associated with the minimum metric and a maximum metric amongstthe metrics of the trellis states.
 19. The method of claim 18, whereinthe control channel receive quality is related to the expressionR=(M₀−M_(min))/(M_(max)−M_(min)), wherein M₀ is the metric of the knownfinal trellis state, M_(min) is the minimum metric amongst the metricsof the trellis states, and M_(max) is the maximum metric amongst themetrics of the trellis states.
 20. The method of claim 18, whereinselecting one of the plurality of control channels depends on anevaluation of the control channel receive qualities further comprises:comparing the computed control channel receive qualities with each otherto determine the control channel having the maximum control channelreceive quality; and selecting that control channel having the maximumcontrol channel receive quality.
 21. A receive unit for selecting acontrol channel from a plurality of control channels, comprising: areceiver configured to receive data transmitted via the plurality ofcontrol channels; a channel quality estimator configured to compute acontrol channel receive quality based on a metric difference between ametric of a known final trellis state and a minimum metric amongst themetrics of the trellis states for each control channel, wherein themetrics are associated with the received data for each respectivecontrol channel; and a selector configured to select a control channeldepending on an evaluation of the computed control channel receivequalities.
 22. The receive unit of claim 21, wherein the channel qualityestimator is configured to compute the control channel receive qualityas a ratio of the metric difference and another metric difference, theanother metric difference being associated with the minimum metric and amaximum metric amongst the metrics of the trellis states.
 23. Thereceive unit of claim 22, wherein the channel quality estimator isconfigured to compute R=(M₀−M_(min))/(M_(max)−M_(min)) for each of theplurality of control channels, wherein R is related to the controlchannel receive quality, wherein M₀ is the metric of the known finaltrellis state, M_(min) is the minimum metric amongst the metrics of thetrellis states, and M_(max) is the maximum metric amongst the metrics ofthe trellis states.
 24. The receive unit of claim 22, wherein theselector comprises: a metrics comparator configured to compare thecomputed control channel receive qualities with each other to determinethe control channel having the maximum control channel receive quality.